The Jaycor Hardened Unit Load Device (HULD) is a high-strength, unibody container for widebody aircraft to confine the blast and suppress the fires caused by internal explosives. Prototype testing has demonstrated that the HULD can contain explosives significantly above the threshold of current detection technology. The device not only conforms to the IATA specifications for these containers, but also promises to provide greater durability due to its extraordinary strength. Combined with existing detection technology, comprehensive protection for airline passengers can be provided. This technology is ready to be put into service to gain operational and durability experience and to enhance passenger safety.
Aviation Security
Commercial aircraft represent vulnerable and attractive targets for terrorist bombing. This unfortunate reality has been dramatized by the downing of a number of commercial aircraft with the loss of all onboard. Faced with this threat, the Federal Aviation Administration (FAA) has invested in the development of various technologies to detect explosive materials and to mitigate the effect of an explosion should detection fail. As indicated in Figure 1, the optimal solution to the problem of aircraft bombing vulnerability involves a balance of structural hardening and detection. As the quantity of explosives to be detected diminishes, the cost of detection becomes unacceptable. Similarly, to harden against a large quantity of explosives is also economically unfeasible. A balance between the two approaches can provide a realistic solution that enhances the level of safety afforded to the traveling public, while minimizing the total security-related costs. The structural hardening of aircraft cargo containers, known as Unit Load Devices (ULDs), represents a practical means of achieving this balance.
Toward this end, the FAA contracted with Jaycor to determine the blast capacity of existing ULDs and evaluate various countermeasures to improve their resistance. These evaluations were performed using analytic models which embodied the essential characteristics of the transient blast loading from the explosive, the response of the ULD to this dynamic loading, and the failure models of the ULD. The evaluations and prototype testing indicated that the resistance of existing containers was minimal.
Figures 2 and 3 below compare the effects of internal explosions form bombs detonated inside ULDs. Figure 2 shows Jaycor's HULD after 2 explosions. Figure 3 shows a ULD, representative of the type used in widebody aircraft, after a small bomb was detonated in one of the suitcases. This bomb was actually below the limit of detection equipment currently in service. The externally propagated blast and fragmentation would have damaged the aircraft. Further, a menacing fire followed this blast, as in all our tests in which the explosion vented from the container.
Figure 2. Jaycor's HULD intact and functioning following two internal explosions from bombs above the current detection threshold.
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Figure 3. Destruction of typical aluminum ULD caused by an internal explosion from a bomb below the current detection threshold.
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Hardening Strategies
Several ULD hardening strategies had been put forward. One strategy proposed wrapping existing ULDs with high-strength materials. This approach is operationally unacceptable to ground crews. Another proposal was to rapidly vent the aircraft. This is not only structurally unacceptable to the airframe manufacturers, but might lead to catastrophic failure of the plane by itself. Many proponents suggested replacing the existing aluminum sides with high-strength materials, but since the panel joints are the weak link, this approach provides marginal protection at a considerable weight penalty. A strategy that has been highly publicized by Royal Ordnance is to allow "controlled" venting of the explosion gasses from the ULD, while maintaining partial structural integrity by an external wrapping. Tests with ULDs have shown that allowing leakage of air following the explosion results in intense fires that threaten the aircraft as much as structural damage.
Only the concept of full blast containment was found to protect against all hazards and it was the only concept the FAA had confidence to fund for development.
The Jaycor HULD
Jaycor considered a host of technologies to achieve total containment and concluded that a unibody design fabricated from lightweight, high-strength, composite material was the most promising. Using computer simulations of the blast process and the structural response, an innovative design for a Hardened ULD (HULD) was developed. The key to the design is the integrated way in which every component of the HULD works together to maintain structural integrity while sealing the container from air flow during the explosion.
The nature of these innovations is such that Jaycor applied for and was awarded basic patents covering the design. These patents are sweeping in nature, not limited to specific container geometries, to specific composite materials, or to specific manufacturing processes. Patent protection is being extended internationally and to additional concepts that provide security to other than widebody aircraft.
Performance
With continued support from the FAA, Jaycor designed and fabricated five prototype HULDs to prove the feasibility and practicality of this countermeasure. These prototypes were made using SPECTRA fibers because of their superior strength-to-weight ratio. These prototypes were fabricated using wet hand lay-up, resin transfer molding, and preimpregnated processes. In Figure 2, the strongest of these containers is shown after confining the blast and suppressing the fire from two explosive tests. The quantity of explosive used in these tests was significantly above the threshold of current detection technology.
Not only does the HULD conform to the specifications required of this class of containers, but the weight of the latest prototype is comparable to that of the population of existing ULDs. The HULD also provides additional benefits over conventional ULDs with a larger door for loading and unloading and greater durability against wear and tear in service. In fact, the sides could not be breached by driving the tines of a forklift into the HULD at full speed.
Introduction Into Service
Now that the blast performance of the HULD has been demonstrated, the prototypes will be placed in service under FAA sponsorship so that refinements based on operations can be made and acceptance by the airlines can be developed. Jaycor has continued to make innovative changes to the design, beyond those in the FAA-sponsored models, that will be incorporated into these prototypes. The HULD is a carefully integrated design in which all of the elements (panel construction, door engagements, material selection) work together to give high strength-to-weight ratio. Evaluation of manufacturing and operational changes arising from this prototype evaluation will be made with analytical and test procedures to ensure that the performance of the HULD is not compromised. Jaycor has established a network of existing and potential fabricators that will be most effectively used.
Prototype testing will establish the practical aspects of blast-proof containers so they can be regulated, produced, and supplied for the protection of airline passengers.
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